1. Field of the Invention
The present invention relates to a control apparatus for an air conditioning system for an electric vehicle which is provided with a cooling / heating cycle that is capable of constituting a cooling cycle and a heating cycle by switching coolant passages.
2. Description of the Related Art
To cite examples of air conditioning systems in the prior art, the air conditioning system disclosed in Japanese Unexamined Patent Publication S59-49439 and Japanese Examined Patent Publication S62-18484 both disclose a heat pump type air conditioning system. Also, in recent years, a system has been disclosed that is provided with a sub condenser downstream of the cooling unit in the air conditioning duct and in which, by switching a three-way valve provided on the intake side of the main condenser, coolant that has flowed out of the compressor is circulated in the following order during cooling operation: from the main condenser to the sub condenser to the cooling unit and finally to the compressor. During heating operation, coolant bypasses the main condenser and so is circulated from the sub condenser to the cooing unit and then to the compressor in that order.
This means that in this system, the coolant discharged from the compressor releases heat into the air and becomes liquefied while it passes through the main condenser during cooling operation. As a result, the coolant that passes through the sub condenser is at a low temperature and the heating quantity by the sub condenser is reduced. Also, in this system, the mixing door fully closes off the front sur face of the sub condenser in order to reduce its effect on the air that passes through the air conditioning duct and air that has been cooled at the evaporator is discharged directly into the cabin.
Now, during heating operation, the coolant discharged from the compressor bypasses the main condenser and is supplied to the sub condenser where it releases heat to the air that passes through. This air is at a low temperature, since its heat has been absorbed as it passed through the evaporator, but the heating performed by the sub condenser is greater than the absorption by the evaporator by the amount of work done by the compressor. Overall, therefore, the air inside the air conditioning duct is heated.
In the air conditioning system for an electric vehicle that has been explained so far, the temperature control lever for setting the air conditioning mode is usually a slide switch that is provided with, for example, a cooling operation zone on the left side, a heating operation zone on the right side and a ventilation zone in the middle. Because of this, when the air conditioning mode is switched from, for example, heating operation to cooling operation, or from cooling operation to heating operation, the slide switch passes through the ventilation operation zone, briefly setting the air conditioning mode to the ventilation mode. As a result, the compressor is turned off, and due to the forcible stop control which is set to prevent a differential pressure activation, it remains off for a specific length of time (normally 3 minutes), generating a temperature difference between the air discharged before the compressor is turned off and the air discharged when the compressor is restarted after it has been off. This presents a problem in that smooth switching of the air conditioning mode is prevented.